Cancel with problem with buyer's address. Return the funds. Arrange with the buyer when you can relist so that they will buy it and pay for it and you can mail it out promptly. Explain to buyer why sellers can no longer provide this customer service that a buyer sometimes needs.
The other possible solution is for the buyer to place a hold on their mail until they return from their vacation. This one makes the most sense but some buyers are not aware that the post office can hold the mail for them.
